Electric fuse



23, 1943- G. R. SERFLING ET AL 2,337,937

ELECTRIC FUSE Filed Sept. 11, 1941 MOLDED 0Q DIE CA6 T MATERIAL lNDI CIA MOL 050 IN END OF TERMINAL Inventors: George Rserfling,

Their- Attorney.

inatented Dec. 2%, M43

sures ELECTRIC FUSE York Application September 11, 1941, Serial No. 410,382

Claims.

Our invention relates to electric fuses and particular to improvements in the construction and method of construction of enclosed high-voltage fuses of the current-limiting type.

Current-limiting fuses consist in the main of a fusible element in the form of one or more conductors of suitable metal, such as silver or zinc, embedded in a granular inert or refractory arcextinguishing material of high dielectric strength, such as sand or relatively finely divided quartz. In most of the commercial currentlimiting fuses, the conductor or conductors are wound on a suitable supporting core of high temperature resistant ceramic material. To these parts are added an enclosing housing and terminals for the conductors.

The process of assembling current-limiting fuses of this type has heretofore required a lazge number of steps and it would be desirable to be able to reduce greatly the assembly operations by simplifying the construction with the conseuent reduction in cost of such fuses without in any way impairing the operating characteristics thereof.

Accordingly, it is an object of our invention to provide a new and improved fuse construction which not only performs very satisfactorily in every respect but which is simple and rugged in construction and considerably less complicated to manufacture.

It is a further object of our invention to provide a new and improved process for assembling fuses of the current-limiting type.

It is another object of our invention to provide a new and improved fuse construction in which the end cap of the fuse is sealed to the fuse centainer by molding or die casting a ferrule of metal about one end of the fuse container to form the fuse terminal.

Still another object of our invention is to provide a new and improved means of centering the fuse wire of a current-limiting fuse without the supporting core usually required by the prior-art constructions.

Further objects and advantages of our invention will become apparent asthe following description proceeds and the features of novelty v which characterize our invention will be pointed 2 is an exploded view of the parts of the fuse shown in Fig. 1, Fig. 3 is a view partly in section to indicate the assembly of the fuse during the manufacturing process, Fig. 4 is an enlarged view of one of the parts of the fuse shown in Figs. 1

to 3, Figs. 5 and 6 illustrate two different steps in the process of manufacturing a current-limiting fuse embodying our invention, and Fig. 7 illustrates a partial sectional view of a fuse device embodying a modification of our invention.

Although, as will be evident to one skilled in the art, certain parts of the present invention may be practiced to advantage with different types and forms of electric fuses, the invention lends itself most advantageously to practice with the enclosed type of fuse, such as is disclosed and claimed in United States Letters Patent No. 2,157,907, granted May 9, 1939, upon an application of K. A. Lohausen, and assigned to the same assignee as the present application, wherein the fusible conductor is shown as being enclosed in a tubular casing of suitable insulating material and surrounded by or embedded in a pulverulent or sandy arc-quenching material.

Referring now to the drawing, we have illustrated an electric fuse device which has a housing structure or casing ill of open ended tubular I form constructed of suitable insulating material,

such as glass or fiber. A suitable fuse link, generally indicated at i l, is mounted within tubular casing it. This fuse link may, if desired, embody the construction disclosed and claimed in the above-mentioned United States Letters Patcut so as to include a central section of reduced cross section, thereby providing more satisfac tory operation. Although the particular size of cross-section of the fuse wire and the material from which it is made form no part of the present invention, we have found that we obtain very desirable operating characteristics by constructing the fuse link or fusible element ii, best shown in Fig. 2, with an insert 92 of a high resistance wire of suitable cross-sectional a ea while the two end portions it of the fuse link i! may be formed of a low resistance wire, such as silver, having a somewhat larger cross section than the insert Q2. The insert i2 is maintained in conductive relation with the end sections 3 of fuse i l by soldering or the like as indicated at M.

The ends of the fusible element ii are preferably looped or folded back upon themselves for a short distance and twisted as indicated at 15, and each of these twisted portions is bent in the form of a U whlchhas a central portion l6 of a length substantially equal to one half the outside diameter of tubular housing or casing I as will be describedin greater detail hereinafter.

In order to maintain the ends of the fuse link II at the central axis of tubular casing l0, we

have provided a fuse link attachment plate I! for each end of tubular housing 10 which includes a small central opening l8 through which the fuse link H may extend. Each plate I! is also provided with a somewhat larger opening I 9 through which the tubular casing ID may be filled with the granular arc-quenching material after the fuse link II is supported therein as shown in Fig. 3.

We have discovered that the central core usually required for centering the fuse link in the prior art constructions during the process of filling the tubular casing with the inert granular material may be dispensed with if the fuse link is formed as a helix with the generating radius thereof decreasing near the ends of the fuse link. With such a construction, we havefound that, when the fuse link is under a slight tension'as in Fig. 3, the tensile forces applied thereto act along the axis of the helix so that the fuse link tends to remain centered within tubular housing ID.

-In order to close the open ends of tubular casing or housing I0 after the fuse link and fuse link attachment plates have been assembled, we have provided saucer-shaped end closure members or end caps 20, which are adapted to fit over the ends of tubular casing l0. As shown in the drawing, these end caps are provided with an interlocking means illustrated as an offset shoulder 21 and they are adapted to be held in sealed relationship with tubular casing ID by metallic ferrules 22 which are molded or die cast around the end of tubular casing I0 so as to envelop the offset shoulder H f end cap 20 while permitting the major portion of the end cap to remain exposed.

Although we have specifically shown this interlocking means as comprising an offset shoulder 2|, it should be understood that such interlocking means might equally well consist of pin pricks, corrugations, knurling, or grooves of some sort. Furthermore, the inherent irregularities of the end caps 20 might be depended upon for obtaining the desired mechanical grip. Accordingly, any suitable end cap with means for obtaining the desired mechanical interlock when such means are enveloped by the die casting material may be employed in accordance with our invention. The die cast or molded ferrules 22 are also cast around the looped end l of fuse link H which extends outside of tubular casing ID in the manner shown in Figs. 1 and 3 and, accordingly, provide the terminals for the fuse.

Since the major portion of the end caps 20 remain exposed after the molding or die casting operation, suitable indicia may be provided on this surface of the end caps 20, asindicated in Fig. 4, to set forth the fuse size or an other pertinent information.

The new and improved fuse construction described above permits the number of assembly operations required heretofore in fuses of the current-limiting type to be reduced greatly while, at the same time, eliminating the requirement of a ceramic core and other additional parts. The manufacturing process can now be reduced to a few relatively simple steps, one of which requires the forming of the fusible element or fuse link into the helical form, the generating radius of which decreases near the ends. For the particular fuse link H described above in which a more resilient center section 12 is utilized, it is necessary to wind the fuse link on a mandrel 23 shown in Fig. 6 with a reduced central section 24 and tapered end portions 25. The reduced central section 24 is required since the inserted section 12 of the fuse link being more resilient than the end portions must be wound in a smaller diameter helix so that, when removed from th mandrel, the free diameter of the helix composed of the insert will approximate that of the adjacent coils in the end portions (see Fig. 2). The ends of the wire are looped back upon themselves, as indicated at IS in Fig. 2, and, as was mentioned above, the twisted ends of the fuse link are formed in the shape of a U.

The next step in the process includes the placing of the fuse link in the tubular casing ID with the fuse link attachment plates 11 seated on either end thereof. The U-shaped ends are constructed with the central portion ll; of the U having a length substantially equal to one half the outside diameter. of tubular casing I0 so that the looped end of the fuse link may extend for a short distance down along the outside of tubular casin ID as best shown in Figs. 1 and 3. The

end cap is placed over the lower end of tubular housing If) so that the structure is assembled as shown in Fig. 3 and is ready for the filling process. Because the fuse link I l is in the form of a helix, the generating radius of which decreases near the ends, the tensile forces on the ends of the fuse link ll exerted at the central axis of tubular housing In by fuse link attachment plates I! provide a centering action to maintain the fuse link in the center of tubular casing ID.

In order that the casing may be completely filled with the desired inert granular arc-extinguishing material, the fuse link as assembled in Fig. 3 is preferably mounted on a vibrator 26 of any suitable form, as indicated schematically in Fig. 4, and suitable inert granular material from conduit 21 connected to a suitable source, not shown, is'admitted to tubular housing It] through opening IS in the upper fuse link attachment plate IT. A soon as the tubular housing I 0 is filled with the granular arc-quenching material, the upper end cap 20, which may include any suitable indicia, such as is shown in Fig. 4, is placed over the end of casing l0 and, as shown in Fig. 3, a short portion of each end of fuse link i I extends along the outside. wall of tubular casing II).

The final step in the assembly of our new and improved fuse construction comprises molding or die casting the ferrules 22 around the ends of 'tubular casing l0 so as to envelop the interlock- I ing means specifically illustrated as oifset'shoulders 2| of end caps 20 and hold them in sealed relationship with housing H] as well as to form good electrical contact with th ends of fuse link ll protruding out of housing l0 and provide the terminals of the fuse device in a manner well understood by those skilled in the art. The suitable indicia on end caps 20 remain visible after the die casting or molding operation since the major portion of each end cap 20 is exposed and the die cast metal merely grips the interlocking means illustrated as the offset shoulder 2!.

Although we have shown a fuse device including an end closure member 20 which is'held in it should be understood that a molding or die casting operation may be used in which the metal would flow somewhat inside the casing as shown in Fig. 7, the corresponding parts of which are designated by the same reference numerals as in Figs. 1 and following. In Fig. 7, the tubular casing is provided with an annular recess id upon which fuse link attachment plate ll may be seated. With this arrangement, the end caps 20 may be entirely eliminated and the die cast ferrule 22', as shown in Fig. 7, constructed to surround completely the ends of tubular casing ill" to seal the casing as well as to provide an electrical terminal for the fuse. In this case, the mold for the die casting operation may be provided with suitable indicia so that the desired indicia will appear on the ends of ferrule it? upon completion of the die casting operation as indicated in Fi i.

From the foregoing, it will be seen that the improved fuse construction while being of simple and rugged construction greatly simplifies the manufacturing processes with consequent cost reduction and provides a very satisfactory fuse in every respect.

Although we have elected to describe and illustrate herein a preferred embodiment of our invention as employed in a fuse device as well as the process of construction thereof, it is contemplated that other applications of our invention to fuses or like electrical devices other than the particular form illustrated will suggest themselves to those skilled in the art. it is intended that such other applications or modifications as do not depart from the true spirit and scope of our invention shall be covered by the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a fuse device, the combination of a housing structure including a tubular casing with an open end, an end cap including interlocking means for closing the end of said casing, a fuse link in said casing, and means for retaining said end cap in sealed relationship relative to said casing including a molded ferrule of conducting material arranged about the end of said casing so as to envelop said interlocking means while permitting the major portion of said end cap to be exposed, said fuse link having an end thereof effectively extending out of said casing so as to be molded into said ferrule and electrically connected therewith.

2. A fuse device having a housing structure including a tubular casing with an open end, a fuse link in said casing extending slightly outside said casing, an end cap including interlocking means thereon for closing the end of said casing but permitting said fuse link to extend there'- from, and means for retaining said end cap in sealed relationship relative to said casing including a molded ferrule of conducting material arranged about the end of said casing so as to envelop said interlocking means on said end cap and the portion of said fuse link extending outside of said casing so as to make electrical connection with said fuse link to provide a terminal for said fuse device while permitting the major portion of said end cap to be exposed.

3. A fuse device having a housing structure including a tubular casing with an open end, an end cap including suitable indioia and interlocking means thereon for closing the end of said casing, a fuse link in said casing, and means for retaining said end cap in sealed relationship relativ to said casing including a molded ferrule of conducting material arranged about the end of said casing so as to envelop said interlocking means without interfering with the indicia on said end cap, said fuse link having an end portion effectively extending out of said casing so as to be molded into said ferrul and electrically connected therewith.

4. In a fuse device, the combination of a housing structure including a tubular casing of insulating material having an open end, an end closure cap for said casing including an offset shoulder thereon, a fuse link in said casing, and means including a molded metallic ferrule electrically connected to one end of said fuse link arranged about the end of said casing to grip said end cap at said offset shoulder and hold it in sealed relationship relative to said casing while permitting the major portion of said end cap to be exposed, said fuse link having an end portion effectively extending out of said casing so as to-be molded into said ferrule and electrically connected therewith.

5. A fuse device having a housing structure including a tubular casing with an open end, a fuse link attachment plate for the end of the casing,

a fuse link in said casing extending through an opening in said plate, an end cap including interlocking means for closing th end of said casing, and means for retaining said end cap in sealed relationship relative to said casing including a molded ferrule of conducting material arranged about the end of said casing so as to surround said interlocking means on said end cap and provide a terminal for said fuse device, the portion of said fuse link extending through said opening in said plate being molded into said ferrule so as to be electrically connected therewith.

6. A fuse device having a housing structure including a tubular casing with an open end, a fuse link attachment for the end of said casing, a fuse link in said casing extending through an opening in said plate, an end cap having suitable indicia and interlocking means thereon for closing the end of said casing, and means for retaining said end cap in sealed relationship relative to said casing including a molded ferrule of conducting material arranged about the end of said casing so as to envelop said interlocking means without interfering with the indicia on said end cap, the portion of said fuse link extending through said opening in said plate being molded into said ferrule so as to be electrically conconnected therewith.

7. In a fuse 0f the current-limiting type, the combination of an open ended tubular casing, a body of inert granular refractory arc-quenching material of high dielectric strength contained within said casing, an elongated fusible element.

embedded in said material in said casing, an end cap having interlocking means thereon for closing the end of said casing, and means for retaining 8. In a fuse of the current-limiting type, the

combination of an open ended tubular casi a body of inert granular refractory arc-quench mg material of high dielectric strength contained within said casing, an elongated fusible element embedded in said material in said casing, an end cap including suitable indicia thereon and having an offset shoulder for closing the end of said casing, and means for retaining said end cap in sealed relationship relative to said casing includinga molded ferrule of conducting material arranged about the end of said casing so as to envelop said offset shoulder without interferrinig, with the indicia on said end cap, said fuse link having an end portion effectively extending out of said casing so as to be molded into said ferrule and electrically connected therewith.

9. In a fuse of the current-limiting type, the combination of an open ended tubular casing, a body of inert granular refractory arc-quenching material of high dielectric strength contained 7 within said casing, an elongated fusible element embedded in said arc-quenching material in said casing, a fuse link attachment plate for the end of said casing including an opening through which said fusible element may extend, an end cap having an oifset shoulder for closing the end of said casing, and means for retaining said end cap in sealed relationship relative .to said casing including a molded ferrule of conducting materia1 arranged about the end of said casing so as to surround said offset shoulder on said end cap and provide a terminal for said fuse device, the portion of said fuse link extending through said opening in said plate being molded into said ferrule so as to be electrically connected therewith.

10. In a fuse device, the combination of a hous ing structure including a tubular casing with an open end, a fuse link in said casing, a fusesupporting means at said open end of said casing, and end closure means for said tubular casing comprising a molded ferrule of conducting material arranged about the end of said casing in sealed relationship thereto and constructed so that suitable indicia relating to saidfuse device are provided on said end closure means, said fuse link having an end portion eifeotively extending out of said casing so as to be molded into said ferrule and electrically connected therewith.

GEORGE R. SERFLING. CARL L. SCHUCK. 

